But coins are "Constitutional".
The Constitution does authorize the "coining of money" (Article I, Section 8). It does not authorize the "printing of fiat currency." How the Court got this one wrong is beyond me. Powerful interests at work here.
Well - as long as you're travelling on that road, they didn't mean the "coining" of nearly worthless slugs. Even silver dollars were only legal tender for debts up to 5 dollars.